Water-absorbing resins are widely used in sanitary goods, diapers, hygienic goods, wiping cloths, packaging materials, water-retaining agents, dehydrating agents, sludge coagulants, disposable towels and bath mats, disposable door mats, thickening agents, disposable litter mats for pets, condensation-preventing agents, and release control agents for various chemicals. Water-absorbing resins are available in a variety of chemical forms, including substituted and unsubstituted natural and synthetic polymers, such as hydrolysis products of starch acrylonitrile graft polymers, carboxymethylcellulose, crosslinked polyacrylates, sulfonated polystyrenes, hydrolyzed polyacrylamides, polyvinyl alcohols, polyethylene oxides, polyvinylpyrrolidones, and polyacrylonitriles.
Such water-absorbing resins are termed “superabsorbent polymers,” or SAPs, and typically are lightly crosslinked hydrophilic polymers. SAPs are materials that imbibe or absorb at least 10 times their own weight in aqueous fluid and that retain the imbibed or absorbed aqueous fluid under moderate pressure. The imbibed or absorbed aqueous fluid is taken into the molecular structure of the SAP rather than being contained in pores from which the fluid could be eliminated by squeezing. Some SAPs can absorb up to 1,000 times their weight in aqueous fluid. SAPs are generally discussed in Goldman et al. U.S. Pat. Nos. 5,669,894 and 5,559,335, and by Mitchell in U.S. Pat. No. 7,249,632, the disclosures of which are incorporated herein by reference. SAPs can differ in their chemical identity, but all SAPs are capable of absorbing and retaining amounts of aqueous fluids equivalent to many times their own weight, even under moderate pressure. For example, SAPs can absorb one hundred times their own weight, or more, of distilled water. The ability to absorb aqueous fluids under a confining pressure is an important requirement for an SAP used in a hygienic article, such as a diaper.
Rebre, in U.S. Pat. Nos. 5,442,014 and 5,373,066, describes the treatment of a certain superabsorbent polymer (“SAP”) with hydrogen peroxide during its manufacture. Treatment with hydrogen peroxide apparently reduces the residual monomer content in the SAP product to an acceptable level. The amount of hydrogen peroxide is from 0.08% to 0.19% by weight relative to the dry SAP polymer.
Metal peroxides, or complexes of metallic salts and hydrogen peroxide (“HP”), have been mentioned as antimicrobial treatments for textiles. These compositions may be formed by the reaction of metal salts such as zinc acetate, with hydrogen peroxide in aqueous solution (U.S. Pat. Nos. 5,656,037; 5,152,996; 4,199,322; and 4,174,418).
The industry of superabsorbents (SAPs) is very often confronted with a need to add other properties to these products in addition to their absorption and retention performance qualities. For example, when the absorbent article in place is impregnated with bodily fluids, in particular urine, it gives off powerful and unpleasant odors, e.g. ammoniacal odors arising from the hydrolysis of urea by the bacterial ureases present on the skin and in the digestive tract. With the aim of eliminating these odors from certain SAP products, certain antiodor additives have been taught. Thus, WO 98/20915 and EP 739 635 describe mixtures containing, respectively, zeolites and borax. U.S. Pat. No. 4,842,593 describes diapers containing SAP with pad agents and a nontoxic, nonirritant and nonvolatile antimicrobial agent which is not incorporated in a non-leachable manner.